Grains such as corn, wheat and sorghum are harvested in large quantities, and are stored prior to a subsequent conversion into products such as flour or molasses Harvested grains contain about 20-25% moisture, which is sufficient to promote fungus and mold growth and cause spoilage of the stored grain.
One method of preserving stored grain is by rapid drying of the grain with a stream of hot air to a moisture content below about 15%. This method has the disadvantage of a high energy cost.
Another method of preserving grain is by incorporation of about 1-2% of propionic acid. However, the treated grain has an objectionable taste and color, and the grain is limited to utility as animal fodder.
Other methods of treating bulk grain as a means of preventing spoilage involve the use of various gases which exhibit pesticidal activity when introduced into enclosed crop storage containers such as bins, elevators and freight cars.
Ammonia gas is an effective preservative when trickled through stored grain. The grain is discolored by the treatment, so that subsequent use is limited to animal consumption.
Sulfur dioxide gas also exhibits preservative effects on treated grain, but the gas adversely affects flavor, and the gas is highly corrosive to metal storage facilities.
Other harvested crop products such as fruits and vegetables similarly require protection against spoilage caused by fungus and other microorganisms during storage and long distance transportation. Lemons, oranges, grapefruit, melons, onions, tomatoes and potatoes are particularly susceptible to decay arising from microbial growth.
One effective method of preserving fruits and vegetables in storage is by treatment with nitrogen trichloride gas. The method requires critical control of the gas concentration to prevent damage to the treated product A serious disadvantage of nitrogen trichloride, and other preservative reagent gases such as chloride and chlorine dioxide, is high acidity in the presence of moisture, which is corrosive to metal storage equipment.
Methods and equipment for preserving stored crop products are described in U.S. Pat. Nos. 1,777,044; 2,715,582; 2,955,940; 4,078,480; 4,208,443; 4,209,538; 4,411,918; 4,421,774; 4,515,266; and references cited therein.
There is continuing interest in the development of new and improved methods for preventing spoilage of harvested agricultural crops during storage and transportation.
Accordingly, it is an object of this invention to provide a method of preserving a harvested crop product which is economical in practice and is long term effective.
It is another object of this invention to provide a method for inhibiting spoilage of a stored food crop which does not adversely affect the appearance and flavor of the crop product.
It is a further object of this invention to provide a method of preserving a newly harvested grain, fruit or vegetable crop in a storage enclosure, which in practice is harmless to the environment and maintains the crop product in a safe condition for human consumption.
Other objects and advantages of the present invention shall become apparent from the accompanying description and examples.